Engines may utilize hydrogen fuel injection to improve fuel economy and/or emissions. In one approach, port fuel injection of hydrogen may be used, where gaseous fuel is delivered to an intake port of each cylinder. With port fuel injection, the injection event may be set to begin after forward air flow in the cylinder (which occurs after intake valve opening and piston downward movement on the intake stroke), and the injection event may be set to end at approximately bottom dead center of the intake stroke. Such a setting reduces the potential for easily ignitable hydrogen to be present in the intake port or manifold for exposure to hot exhaust residual/hot combustion chamber metal surfaces for the subsequent engine cycle.
However, as engine speed increases, a given injection amount, or pulsewidth, may result in a proportionally greater injector duty cycle as a function of crank angle. If the injection duration is longer than the intake duration (e.g., longer than the intake stroke, and/or longer than intake valve opening), hydrogen may be present in the intake port before intake valve opening of the following engine cycle. Further, such hydrogen can be prone to igniting due to hot gases/metal temperature, potentially causing an undesirable intake backfire.
One approach to address such situations is to improve the bandwidth of the hydrogen injectors. However, while higher bandwidth injectors may be helpful, they still may not have the bandwidth to control the injection event to only occur during the intake event under all conditions. For example, the injector bandwidth may be insufficient to provide such control at low speeds and loads as well as at high speeds and loads.
Another approach to address such situations is to first cool the cylinder with fresh air having little to no hydrogen fuel, and then subsequently deliver pre-mixed air and hydrogen. Such operation may be achieved with a bifurcated intake port leading to separated intake valves, where the timing of the intake valve openings of the valves are staggered relative to one another.
In this way, it is possible to reduce backfires since initially fresh air free of hydrogen cools the charge, so that when the hydrogen enters the cylinder, it does not contact overly hot surfaces or other charge.
Note that the above examples are merely for introductory purposes, and the various examples and embodiments described herein are not limited to such situations.